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arXiv · 2105.13207

Galois module structure of square power classes for biquadratic extensions

Frank Chemotti·Jan Minac·Andrew Schultz·John Swallow
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Abstract

For a Galois extension $K/F$ with $\text{char}(K)\neq 2$ and $\text{Gal}(K/F) \simeq \mathbb{Z}/2\mathbb{Z}\oplus\mathbb{Z}/2\mathbb{Z}$, we determine the $\mathbb{F}_2[\text{Gal}(K/F)]$-module structure of $K^\times/K^{\times 2}$. Although there are an infinite number of (pairwise non-isomorphic) indecomposable $\mathbb{F}_2[\mathbb{Z}/2\mathbb{Z}\oplus\mathbb{Z}/2\mathbb{Z}]$-modules, our decomposition includes at most $9$ indecomposable types. This paper marks the first time that the Galois module structure of power classes of a field has been fully determined when the modular representation theory allows for an infinite number of indecomposable types.

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Frank Chemotti, Jan Minac, Andrew Schultz, John Swallow. 2021-05-27. Galois module structure of square power classes for biquadratic extensions. https://doi.org/10.4153/s0008414x22000165

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